Note that the points discussed below are not necessarily admitted to be prior art.
China is rich in tight oil and gas resources. With the continuous improvement of exploration and development technology, especially the breakthrough of horizontal well volumetric fracturing technology, the pilot test of the tight oil development has been conducted in Changqing Oilfield, Daqing Oilfield, Tuha Oilfield and the like. Horizontal well volumetric fracturing has become the core technologies for the development of tight reservoirs, but their utilization of reservoirs is still limited. According to geological analysis, the rock wettability of tight reservoirs is generally neutral-lipophilic reservoirs. Rock wettability is one of the important factors that control the oil-water distribution, quantity and flow-driven-displacement mechanism in the reservoir. The change of wettability directly affects the capillary pressure, oil-water relative permeability, water-driven state, the number of bound phases and the distribution of residual oil saturation of the reservoir and the electrical characteristics of the reservoir. Therefore, changing the wettability of the reservoir is one of the reliable methods of increasing the mobilization capacity of the reservoir and crude oil recovery.
Wettability inversing agents that change reservoir wettability are commonly used to increase waterflooding, reduce waterflood pressure, and indirectly increase oil recovery by increasing stratum pressure during oilfield development. At the same time, there are mainly three kinds of wettability inversing surfactants for oilfields in domestic and foreign research: (1) cationic surfactants, the most commonly used is alkyl trimethyl ammonium bromide (CTAB); (2) anionic surfactants, mainly is polyoxyethylene (propylene) alkyl alcohol ether sulfate ester salt or sulfonate; (3) non-ionic surfactants, mainly polyoxyethylene alkyl phenol ethers. Among them, quaternary ammonium surfactants (such as CTAB) will make oil-wet reservoirs and thus reduce the relative permeability of hydrocarbons in rocks. Anions (such as petroleum sulfonate) have poor salt-tolerance ability, high critical micelle concentration, and high loss due to interaction with multivalent ions in the stratum; non-ionic surfactant in the stratum has a poor stability, poor high temperature resistance and high prices.